The new software would require that any incoming e-mail from an unfamiliar address — one not in a user's address book — prove that it isn't spam, Gates said.Microsoft's challenge-based email software certainly has promise, but I just don't see it killing off spam in the next two years. I would, however, love to be proven wrong.
One possible approach would send a puzzle back to the sender. The puzzle would be designed so that only a human could solve it. The e-mail would be accepted only if the puzzle were solved.
With a story like this, it's tempting to quote Gate's infamous assertion that no one would ever need more than 640k of memory on a computer. Gates, however, denies ever uttering such a thing. Let's hope someone got his spam prediction on tape.